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Admissibility for a Class of Quasiregular Representations

Published online by Cambridge University Press:  18 June 2019

Bradley N. Currey
Bradley N. Currey*
Affiliation:
Department of Mathematics and Computer Science, Saint Louis University, Saint Louis, MO 63103, U.S.A. email: curreybn@slu.edu
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Abstract

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Given a semidirect product $G\,=\,N\,\rtimes \,H$ where $N$ is nilpotent, connected, simply connected and normal in $G$ and where $H$ is a vector group for which $ad(\mathfrak{h})$ is completely reducible and $\mathbf{R}$-split, let $\tau $ denote the quasiregular representation of $G$ in ${{L}^{2}}(N)$. An element $\psi \,\in \,{{L}^{2}}(N)$ is said to be admissible if the wavelet transform $f\,\mapsto \,\left\langle f,\,\tau (\cdot )\psi \right\rangle $ defines an isometry from ${{L}^{2}}(N)$ into ${{L}^{2}}(G)$. In this paper we give an explicit construction of admissible vectors in the case where $G$ is not unimodular and the stabilizers in $H$ of its action on $\hat{N}$ are almost everywhere trivial. In this situation we prove orthogonality relations and we construct an explicit decomposition of ${{L}^{2}}(G)$ into $G$-invariant, multiplicity-free subspaces each of which is the image of a wavelet transform . We also show that, with the assumption of (almost-everywhere) trivial stabilizers, non-unimodularity is necessary for the existence of admissible vectors.

Keywords

22E2722E30
Type
Research Article
Information
Canadian Journal of Mathematics , Volume 59 , Issue 5 , 01 October 2007 , pp. 917 - 942
Copyright
Copyright © Canadian Mathematical Society 2007

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